1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a semiconductor device, which is suitable to form a thin film that is stable at a high temperature.
2. Discussion of the Related Art
As semiconductor devices become smaller from 0.25 micron class to 0.18 and 0.13 micron classes, their sheet resistivity increases and becomes a problem. In order to solve this problem, presently cobalt silicide is widely used which shows a lower resistance than titanium silicide in a micron pattern.
A related art method for fabricating a semiconductor device will be explained with reference to the attached drawings. FIGS. 1A.about.1D illustrate steps of a related art method for fabricating a semiconductor device.
Referring to FIG. 1A, a field oxide film 12 is formed on a field region of a semiconductor substrate 11 having the field region and an active region defined thereon. A gate insulating film 13 and a gate electrode polysilicon film (not shown) are formed in succession on an entire surface of the semiconductor substrate 11, and subjected to photolithography and etching, to remove the polysilicon film and the gate insulating film 13 selectively and form a gate electrode 14. The gate electrode 14 is used as a mask in implanting impurity ions in the entire surface of the semiconductor substrate 11 lightly, to form LDD (Lightly Doped Drain) regions 15 in the surface of the semiconductor substrate 11 on both sides of the gate electrode 14.
As shown in FIG. 1B, an insulating film is formed on an entire surface of the semiconductor substrate 11 inclusive of the gate electrode 14. The insulating film is then etched back to form insulating sidewalls 16 at both sides of the gate electrode 14. Then, the gate electrode 14 and the insulating film sidewalls 16 are used as masks in implanting source/drain impurity ions (As.sup.+ or P.sup.+) in an entire surface of the semiconductor substrate 11 heavily, to form source/drain impurity regions 17 in the surface of the semiconductor substrate 11 on both sides of the gate electrode 14 connected to the LDD regions 15.
As shown in FIG. 1C, a cobalt film 18 and a titanium nitride film TiN 19 are formed on an entire surface of the semiconductor substrate 11 in succession, and, as shown in FIG. 1D, subjected to annealing at approximately 500.degree. C., to cause reaction between the cobalt film 18, the gate electrode 14 and the semiconductor substrate 11, thus forming a cobalt silicide film 20. In this instance, the titanium nitride 19 is provided for blocking an influence from oxygen when the cobalt reacts with the silicon by annealing. The titanium nitride film 19 is in general formed in-situ without vacuum break after the formation of the cobalt film 18. The titanium nitride film 19 and the remaining cobalt film 18, which both had no reaction with the semiconductor substrate 11 and the gate electrode 14, are wet etched and removed using a mixed solution of H.sub.2 SO.sub.4 :H.sub.2 O.sub.2 or NH.sub.4 OH:H.sub.2 O.sub.2 and a mixed solution of HCL:H.sub.2 O.sub.2 :H.sub.2 O, and subjected to annealing at approximately 700.about.800.degree. C., to lower a resistance of the cobalt silicide film 20. The annealings are conducted at a low temperature for the first time and at a high temperature for the second time in formation of the cobalt silicide film 20 to form a cobalt silicide film 20 with a low resistance because the high temperature annealing forms the cobalt silicide film even at sides of the insulating film sidewalls 16.
However, the related art method for fabricating a semiconductor device has the following problems.
First, the formation of the cobalt silicide film by annealing consumes the substrate excessively, and partial excessive formation of the cobalt silicide film causes an excessive flow of leakage current at a shallow junction that is inevitable when devices are scaled down.
Second, the titanium nitride film only blocks an influence from oxygen, but can not prevent the consumption of the substrate caused by cobalt.
Third, a thin film of cobalt silicide, formed by forming a cobalt film on a polysilicon film of fine grain size and subjecting to annealing, is unstable and susceptible to heat because cobalt atoms can migrate to a lower portion of the polysilicon film along grain boundaries of the polysilicon film.